Thanks for the link! I just figured it would use the simplest solution that could get the job done. I don't know how important measuring foot slip/ground contact is for quadrupedal locomotion or how well it can be approximated by measuring joint angles and computing forward kinematics. I guess load cells are cheap so why not use them?

Again, thanks for digging that up. It's heaps better than idle speculation.

Getting the job done is important! A simple solution is no good if it doesn't work. Presumably they need to know where the ground is / how firm the ground is, before putting all it's weight down. There is a good bit in the video of it climbing over rubble.